If a centrifuge be at one’s disposal, the boiling water is centrifuged at a suitable speed. This is still more necessary when one is working with finely minced organs or bacteriological cultures and the like, otherwise too much of the material would be lost when pouring off the water.
After the sixth boiling only five times the amount of water at most is used. The smaller the amount of water employed, the more exact is the result of the test for the extractive substances that react with ninhydrin. In every case as much water must be present as will be needed to continue active boiling for five minutes without the risk of burning, the smallest possible vessels being used. Then a certain quantity of boiled water is filtered through a hardened filter paper. To 5 c.c. of the filtrate is added at least 1 c.c. of a 1 per cent. aqueous solution of ninhydrin, and the mixture is boiled (as described on p. 160 seq.) for one minute. If, after half an hour, not the slightest trace of a violet coloration manifests itself, the organ may be considered as suitable, provided it still remains snow—white. Only the tissues of the liver, the spleen, and the kidneys do not appear quite white. Should the tissue turn grey, or even brown, during boiling, this is a proof that it was not absolutely freed from blood, or that the boiling was not conducted properly. Should the particular test prove positive, the boiling must be continued—i.e., the water must be poured
